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12.14: Introduction to Evidence for Evolution - Biology

12.14: Introduction to Evidence for Evolution - Biology


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What you’ll learn to do: Describe how the theory of evolution by natural selection is supported by evidence

The evidence for evolution is compelling and extensive. Darwin dedicated a large portion of his book, On theOrigin of Species, to identifying patterns in nature that were consistent with evolution, and since Darwin, our understanding has become clearer and broader.

The video below summarizes the major types of evidence supporting evolution; you will read more details in the pages that follow.

A YouTube element has been excluded from this version of the text. You can view it online here: pb.libretexts.org/bionm1/?p=458


What is the evidence for evolution?

Evolution is a scientific theory supported by an overwhelming amount of evidence. Some Christians fear that accepting the theory means rejecting God as creator. But that just doesn’t follow. Christians accept scientific theories about the weather, the formation of mountains, and even the conception and development of individual human beings while still acknowledging that God is the creator and sustainer of these things. So giving a scientific description for a process does not rule out a legitimate theological description of the process as well. This article summarizes multiple independent lines of evidence that evolution is the best scientific description of the process by which life has diversified. Think of each of these lines of evidence as a clue to the past, all of which together form a compelling picture of the relatedness of all species.


Download CBSE class 12th revision notes for chapter 7 Evolution in PDF format for free. Download revision notes for Evolution class 12 Notes and score high in exams. These are the Evolution class 12 Notes Biology prepared by team of expert teachers. The revision notes help you revise the whole chapter 7 in minutes. Revision notes in exam days is one of the best tips recommended by teachers during exam days.

Evolutionary biology is the study of history of life forms on earth. The evolution of life on earth, different changes in flora and fauna around earth that co-exist along with human beings also forms parts of evolution.

Origin of Life

The origin of life is considered unique events in the history of universe. Huge cluster of galaxies comprises the universe. Galaxies contain stars and clouds of dust and smoke.

Big Bang Theory attempts to explain the origin of universe. According to this theory, a huge explosion occurs that forms the different galaxies.

In solar system of Milky Way galaxies, earth has been supposed to be formed about 4.5 billion years ago. There was no atmosphere in early earth. Water vapour, methane, carbon dioxide and ammonia released from molten mass covered the earth surface.

UV rays from sun splits the water into hydrogen and oxygen. Life appeared 500 million years after the formation of earth.

There are different theories regarding the origin of life on earth-

  • Some scientist believes that life comes from other planets. Early Greek thinker thoughts that unit of life is called spores transferred from other planets.
  • According to other theory, life comes out of dead and decaying matters like straw and mud. This theory is called theory of spontaneous origin.
  • Louis Pasture experimentally proved that life arises only from pre-existing life. Spontaneous theory of origin of life is dismissed after that.
  • Oparin and Haldane proposed that the first form of life could have come from pre-existing non-living organic molecules like RNA and protein etc. The formation of life preceded by chemical evolution. At that time condition on earth were- high temperature, volcanic eruption, reducing atmosphere containing CH4and NH3.

Miller experiment of Origin of Life- S.L. Miller in 1953, conducted an experiment to show the origin of life on earth in the physical environment similar to condition prevails at that time.

Miller created similar condition of temperature and pressure in laboratory scale. He created electric discharge in a flask containing CH4, H2 and NH3 and water vapour at 8000C.

He observed formation of amino acids in flask after 15 days of electric discharge. Similar experiment by other scientist found formation of sugars, nitrogen bases, pigments and fats.

Analysis of meteorite content also reveals similar compounds that reveal that similar process are occurring elsewhere in the space. This experimental evidence about the origin of life is called chemical evolution of life.


Debates about evolution

There is very little debate in the scientific community about this broad characterization of evolution (anyone who claims otherwise is either uninformed or deliberately trying to mislead). The observational evidence explained by common ancestry is overwhelming. Of course new data causes scientists to adjust some of the specifics (like how long ago species diverged, or which species are most closely related), but this core view is overwhelmingly supported and agreed upon by the vast majority of scientists in the field.

But that is not to say there are no debates and controversies about evolution among those who accept this core view of the theory. Evolutionary scientists debate the extent to which the variation element is explained by random genetic mutations, and how important other selection mechanisms are beyond reproductive fitness. Scientists have different views on topics like how gradual evolutionary change is and on the details of how natural selection works. And as we’ve already seen, there are significant differences of opinion about how to interpret various aspects of evolution with respect to worldviews, such as whether there is overall direction to evolution, and what the significance of evolution is for theology.

At BioLogos we believe the best contemporary science is consistent with Christian theology. Find more information on evolution and the BioLogos perspective on origins in the other resources on this page or by searching on particular terms in our search box.

Last updated on February 18, 2019

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12.14: Introduction to Evidence for Evolution - Biology

The issue: What restrictions does the First Amendment place on the ability of states and school boards to restrict the teaching of evolution or encourage the teaching of "creation science" in the public school classrooms?

The so-called "Scopes Monkey Trial" of 1925, concerning enforcement of a Tennessee statute that prohibited teaching the theory of evolution in public school classrooms, was a fascinating courtroom drama featuring Clarence Darrow dueling with three-time presidential candidate William Jennings Bryan. However entertaining the trial in Dayton, Tennessee was, it did not resolve the question of whether the First Amendment permitted states to ban teaching of a theory that contradicted religious beliefs.

Not until 1968 did the Supreme Court rule in Epperson vs. Arkansas that such bans contravene the Establishment Clause because their primary purpose is religious. The Court used the same rationale in 1987 in Edwards vs Aguillard to strike down a Louisiana law that required biology teachers who taught the theory of evolution to also discuss evidence supporting the theory called "creation science."

The controversy continues in new forms today. In 1999, for example, the Kansas Board of Education voted to remove evolution from the list of subjects tested on state standardized tests, in effect encouraging local school boards to consider dropping or de-emphasizing evolution. In 2000, Kansas voters responded to the proposed change by throwing out enough anti-evolution Board members to restore the old science standards, but by 2004 a new conservative school board majority was proposing that intelligent design be discussed in science classes. (In 2006, the Kansas tug-of-war continued, with pro-evolution moderates again retaking control of the Board.)

In 2005, attention shifted to Dover, Pennsylvania, where the local school board voted to require teachers to read a statement about intelligent design prior to discussions of evolution in high school biology classes. Eleven parents of Dover students challenged the school board decision, arguing that it violated the Establishment Clause. After a six-week trial, U. S. District Judge John E. Jones issued a 139-page findings of fact and decision in which he ruled that the Dover mandate was unconstitutional. Judge Jones's decision was surprisingly broad. He concluded that "ID is not science," but rather is a religious theory that had no place in the science classroom. Jones found three reasons for his conclusion that intelligent design was a religious, and not a scientific, theory. First, he found ID violated "the self-imposed convention" of the scientific method by relying upon a supernatural explanation for a natural phenomenon, rather that the approach favored in science: testability. Second, ID is based on the same "contrived dualism" as creation science, namely its suggestion that every piece of evidence tending to discredit evolution confirms intelligent design. Jones found ID's "irreducible complexity" argument to be "a negative argument against evolution, not proof of design." Finally, Jones concluded that the expert testimony offered by the defendants in support of ID (generally relating to "irreducible complexity") had been refuted in peer-reviewed research papers. The decision of Judge Jones in Kitzmiller v Dover (2005) is available online:

Conflicts between science and religion will not end any time soon. In the future, legal conflicts between science and religion can be expected over theories such as "The Big Bang," which also undermines Fundamentalist beliefs about creation.

Facts are Stubborn Thing
by Douglas O. Linder

It is hardly surprising that Darwin’s theory of evolution should meet with so much resistance. We encounter an idea that comforts us, an account like Genesis 1 that establishes our specialness, and ask: “Can I believe it?” We consider a thing that troubles us, a process like evolution that seems chance-driven and dethrones us from our special place in the universe, and ask instead: “Must I believe it?”

Evolution suggests that our species, if not quite an accident, is an extreme improbability — and, most likely, one whose time is limited — on life’s continuing and circuitous journey to an undetermined destination. Must we believe it? Darwin knew that many people, raised to believe in miracles or magic, would find his theory hard to swallow. In his autobiography, he noted that, as a young man on the H.M.S. Beagle, he had written in his journal of “the higher feelings of wonder, admiration, and devotion” that would “fill and elevate” his mind. He lamented that now, older and wiser, believing in evolution and disbelieving in God, even “the grandest scenes” evoked no powerful feelings: “I am like a man that has become color-blind.” Publishing his theory, he said, felt “like confessing a murder.”

When William Jennings Bryan took on evolution in a courtroom in Tennessee in 1925, in the famous Scopes “Monkey” trial, he acknowledged that he did not fully understand the theory of evolution, but said that he fully understood the theory’s dangers and misuse: how it threatened to leave students feeling lost in an uncaring universe, how it could lead to sterilization of the abnormal and diminished concern for the survival of the “unfit.” Bryan cheerfully ignored the evidence for evolution, explaining, “I would rather begin with God and reason down than begin with a piece of dirt and reason up.”

I believe in the theory evolution not because I want to, but because I feel I must, and because, unlike Bryan, I find it hard to reason in one direction or another. Creationists have offered one objection after another — “The immune system is too complex to have evolved,” “Evolution could never produce an eye, because what use is half an eye?” — and each has been answered. As the confirming fossil and DNA evidence piles up, as the theory of evolution reveals itself to be a powerful tool for both explaining the imperfections of species and accounting for transitional species, it becomes ever more difficult to believe in the pleasing creation stories told in Genesis and elsewhere. Facts, as John Adams reminded us, are stubborn things. Whether 20 years or 200 years from now, the accumulating evidence will become so overwhelming that evolution will be as accepted as the Sun-centered solar system is today. (No gloating allowed, scientists.)

Our challenge is to accept evolution while maintaining a sense of wonder, concern for those whose survival is beyond their own means, and a vision of a colorful and surprise-filled world.


Biologists teach that all living things on Earth are related. Is there any solid evidence to back this claim? Join us as we explore the facts! We start with a close look at the origin of whales from land mammals, and then touch on the origins of several other critters, including our own species.

Explore Further

Special thanks to Dr. Hans Thewissen and Dr. Philip D. Gingerich for helping edit our script, answer our questions, and for getting us photos of embryos and fossils.

For Teachers

The content of this video meets criteria in the following Disciplinary Core Ideas defined by Next Generation Science Standards. Use our videos to supplement classroom curriculum.

High School, Life Science 3

Heredity: Inheritance and Variation of Traits.

High School, Life Science 4

Biological Evolution: Unity and Diversity.

Georgia Biology 2

How genetic information is expressed in cells.

Georgia Biology 3

How biological traits are passed on to successive generations.

Georgia Biology 5

Interdependence of all organisms on one another and their environment.

Georgia Biology 6

Contributors

Our videos benefit from guidance and advice provided by experts in science and education. This animation is the result of collaboration between the following scientists, educators, and our team of creatives.

  • Jon Perry
  • Jeremiah Deasey
  • Anthony Danzl
  • Rosemary Mosco
  • Jordan Collver
  • Tyler Proctor
  • Zaid Ghasib
  • Katie Hick
Advisors
  • Eric T. Parker, PhD
  • J.G.M. Hans Thewissen, PhD
  • Joy S. Reidenberg, PhD
  • Philip D. Gingerich, PhD
  • Tom Cochran

Corrections

  • Dolphin embryos shown in this animation come from spotted dolphins (they are mislabeled as common dolphins).
  • The adult shown is a dusky dolphin.
  • The source of the photo of a bowhead whale pelvis is mislabeled in the animation. It actually comes from the Department of Wildlife Management, Barrow, Alaska.

Transcript

What is the evidence for evolution?

The theory of Biological Evolution makes two very bold claims about living creatures:

First: All living things on earth are related. They evolved from a common ancestor.

Second: The evolution of living things is powered by natural processes. Things which can be studied and understood.

But is there really any evidence that these two claims are true?

Yes. There are so many observable facts from so many different fields of study that the only way we can even begin to talk about them is to group them into categories or lines of evidence.

To keep things simple, here we’ll focus on Evolution’s first claim that: All living things on earth are related.

We cannot tackle the entire tree of life at once (after all there’s an estimated 8.7 Million species alive today), so instead we’ll focus most of our attention on one fairly small but fascinating branch of the evolutionary tree: Cetaceans. This branch includes whales, dolphins and porpoises.

Biologist claim that all these creatures are closely related, and that the entire group evolved from an ancient 4 legged land mammal.

Instead of taking their word for it, let’s look at the facts. We’ll start with a few from field of comparative anatomy: the study of differences and similarities between living things.

Whales live in water and from a distance, they sort of look like giant fish. A close inspection of their anatomy however, tells us a very different story.

Whales are like land mammals and unlike fish:

  • have placentas and give live birth
  • they feed milk to their young
  • they are warm blooded (which is extremely rare for a fish)
  • and whales do not have gills, instead — just like us — they breath air with two fully developed lungs.

Whales don’t seem to have noses like mammals do. Instead they breathe through blowholes coming out the tops of their heads. Some whales have two blowholes that almost look like nostrils, but dolphins and porpoises only have one. Surprisingly, if you look at their skulls, you find that the blowhole splits into 2 nasal passages inside the head. Could it be that the blowhole is actually a highly modified mammal nose? It looks that way but we’ll need more evidence to be sure.

Many whales have hair, just like land mammals. In this photograph, you can actually see the whiskers of this baby gray whale as he rests his chin on mama’s back.

Strangely, whales have arm, wrist, hand, and finger bones inside their front flippers. Here’s a photo of these bones, the same bones that bats, hippos and people have in their front appendages: One bone, two bones, wrist bones and finger bones.

Modern whales do not have back legs but they do have a pair of strange tiny bones where the hips and hind legs should be. Here’s a picture of these bones from a bowhead whale. They almost look like shriveled hip, thigh, and shin bones. This one even has what looks like a deformed ball and socket joint between the hip and thigh bone, just like the ball and socket joint in your own hip. Is this resemblance a mere coincidence or are these real leg bones? Perhaps leftovers from the whales evolutionary history?

Before we draw any bold conclusions, let’s see if a completely separate line of evidence will confirm our suspicions.

Embryology is the study of how creatures develop before being born or hatching from an egg.

Here we see a dolphin and a human embryo, side by side, at similar stages of development. Notice that they both have what look like arm buds, and leg buds. In humans, the leg buds grow to become legs. In whales, they grow for a while, but then stop, effectively fading away as the rest of the whale continues to grow.

These are all photographs of a common dolphin at different stages of development. Notice that early on, we see two nostril grooves on the front of the face, just like you’d expect in a puppy or a human.

As the dolphin continues to grow, the nostril groves migrate to the top of the head and fuse together becoming the dolphin’s blowhole.

So far we have multiple facts from two independent lines of evidence, comparative anatomy, and embryology, both telling us the exact same story: The ancestors of whales were once 4 legged land creatures! Will the fossil record act as a third witness confirming this idea?

These are two species of extinct basilosaurid whales!

These creatures are known from multiple well preserved skeletons. They appear to have lived side by side roughly 34 to 40 million years ago.

In this photo we are looking down at the top of a basilosaurid skull. This is not a model or a cast, these are the actual bones which were pulled from the ground. Notice that the nasal opening is not on the top of the head like those of modern whales, and not at the end of the snout like those of most land mammals. Instead their nostrils sit right in the middle, this is an intermediate species, exactly what the theory of evolution tells us we should find!

At the back-end of a basilosaurid’s body, there are small, yet fully developed hips, legs, ankle, feet and we suspect they had at least 3 toes though we’ve only found the bones for one.

These legs are far too small for walking on land, but may have been useful for mating or scratching away parasites and itchy skin.

Evolutionary theory tells us that the further we go back in time, the harder it will be to distinguish whales from regular land mammals.

Meet Maiacetus. Scientists have found multiple well preserved skeletons of this species, one of which appears to be a pregnant mother.

The hip bones of Maiacetus do seem sturdy enough to walk on land, but this animal is considered to be a whale for many reasons:
Their skeletons have all been found among fossils of sea-creatures

Their short legs combined with long flat fingers and toes, suggest they were strong swimmers with webbed hands and feet.

Here we see the bottom side of a maiacetus jaw and skull as it looked at the dig site. Her teeth match those of the basilosaurid whales we saw earlier.

And unique structures of her middle ear bones, the bulbs behind her jaw, match those of basilosaurid whales and modern whales.

Maiacetus appears to be, a walking whale!

The fossils of many ancient whale-like mammals have been found, and people continue to find more. Together, these fossils blur the line between 4 legged land mammals and fully aquatic whales, solidifying the idea that whales indeed, evolved from land creatures.

Now lets look at a 4th line of evidence: DNA?

DNA molecules contain chemical codes which act like recipes for living things.

Without ever looking at bones, embryos, or anatomy, researchers can compare the DNA code of different living creatures to find out who is most closely related to who.

Whale DNA has been compared to all kinds of other animals: fish, sea lions, you name it, and so far, the closest genetic match, is to the pudgy, water-loving hippopotamus.

This does not mean that whales evolved from hippos, but if this genetic finding is correct, whales and hippos both evolved from a common ancestor which lived roughly 54 million years ago.

At first the link between whales and hippos surprised researchers. Whales are mainly carnivores – they eat things like fish and small crustaceans, while hippos are mostly vegetarian.

A closer look however, reveals that hippos and whales, actually share many strange features, some of which may have come from their common ancestor.

Ancient walking whales have specially shaped ankle bones, found only in hippos and the close relatives of hippos, hippos, just like whales, often give birth and even nurse their young underwater, they both have multi chambered stomachs (which is common for herbivores but unheard of in fish-eating mammals), they are both missing a coat of fur, and here’s a fun fact – whales and hippos are some of the only mammals on earth that have internal testicles.

So there you have it, dozens of facts from 4 independent lines of evidence, all tell us the exact same story, whales evolved from 4 legged land mammals, but the history of whales isn’t the only evolutionary history that we’ve been able to work out.

We know from fossils, DNA, embryology and many other lines of evidence that bird wings are actually modified arms and claws! Birds evolved from dinosaur-like ancestors.

We can also clearly see that bat wings evolved from 5 fingered hands, similar to those of monkeys and shrews.

We’ve found that humans share a fairly recent common ancestor with chimpanzees, that mammals evolved from reptile-like creatures, those reptile-like creatures evolved from amphibian-like creatures, those amphibian-like creatures evolved from fish-like creatures, and fish if you go back far enough, share a common ancestor with segmented worms.

So to sum things up, thousands of observable facts from completely independent fields of study, are coming together to tell us the exact same story.

All living things on earth are related.

I’m Jon Perry and that’s a basic overview of the evidence for evolution, Stated Clearly.


Five Proofs of Evolution

1. The universal genetic code. All cells on Earth, from our white blood cells, to simple bacteria, to cells in the leaves of trees, are capable of reading any piece of DNA from any life form on Earth. This is very strong evidence for a common ancestor from which all life descended.

2. The fossil record. The fossil record shows that the simplest fossils will be found in the oldest rocks, and it can also show a smooth and gradual transition from one form of life to another.

Please watch this video for an excellent demonstration of fossils transitioning from simple life to complex vertebrates.

3. Genetic commonalities. Human beings have approximately 96% of genes in common with chimpanzees, about 90% of genes in common with cats (source), 80% with cows (source), 75% with mice (source), and so on. This does not prove that we evolved from chimpanzees or cats, though, only that we shared a common ancestor in the past. And the amount of difference between our genomes corresponds to how long ago our genetic lines diverged.

4. Common traits in embryos. Humans, dogs, snakes, fish, monkeys, eels (and many more life forms) are all considered "chordates" because we belong to the phylum Chordata. One of the features of this phylum is that, as embryos, all these life forms have gill slits, tails, and specific anatomical structures involving the spine. For humans (and other non-fish) the gill slits reform into the bones of the ear and jaw at a later stage in development. But, initially, all chordate embryos strongly resemble each other.

In fact, pig embryos are often dissected in biology classes because of how similar they look to human embryos. These common characteristics could only be possible if all members of the phylum Chordata descended from a common ancestor.

5. Bacterial resistance to antibiotics. Bacteria colonies can only build up a resistance to antibiotics through evolution. It is important to note that in every colony of bacteria, there are a tiny few individuals which are naturally resistant to certain antibiotics. This is because of the random nature of mutations.

When an antibiotic is applied, the initial innoculation will kill most bacteria, leaving behind only those few cells which happen to have the mutations necessary to resist the antibiotics. In subsequent generations, the resistant bacteria reproduce, forming a new colony where every member is resistant to the antibiotic. This is natural selection in action. The antibiotic is "selecting" for organisms which are resistant, and killing any that are not.


Natural Selection and Evolution

Clarification Statement: Emphasis is on a conceptual understanding of the role each line of evidence has relating to common ancestry and biological evolution. Examples of evidence could include similarities in DNA sequences, anatomical structures, and order of appearance of structures in embryological development.

Assessment Boundary: none

Construct an explanation based on evidence that the process of evolution primarily results from four factors: (1) the potential for a species to increase in number, (2) the heritable genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for limited resources, and (4) the proliferation of those organisms that are better able to survive and reproduce in the environment. HS-LS4-2

Clarification Statement: Emphasis is on using evidence to explain the influence each of the four factors has on number of organisms, behaviors, morphology, or physiology in terms of ability to compete for limited resources and subsequent survival of individuals and adaptation of species. Examples of evidence could include mathematical models such as simple distribution graphs and proportional reasoning.

Assessment Boundary: Assessment does not include other mechanisms of evolution, such as genetic drift, gene flow through migration, and co-evolution.

Apply concepts of statistics and probability to support explanations that organisms with an advantageous heritable trait tend to increase in proportion to organisms lacking this trait. HS-LS4-3

Clarification Statement: Emphasis is on analyzing shifts in numerical distribution of traits and using these shifts as evidence to support explanations.

Assessment Boundary: Assessment is limited to basic statistical and graphical analysis. Assessment does not include allele frequency calculations.

Construct an explanation based on evidence for how natural selection leads to adaptation of populations. HS-LS4-4

Clarification Statement: Emphasis is on using data to provide evidence for how specific biotic and abiotic differences in ecosystems (such as ranges of seasonal temperature, long-term climate change, acidity, light, geographic barriers, or evolution of other organisms) contribute to a change in gene frequency over time, leading to adaptation of populations.

Assessment Boundary: none

Evaluate the evidence supporting claims that changes in environmental conditions may result in: (1) increases in the number of individuals of some species, (2) the emergence of new species over time, and (3) the extinction of other species. HS-LS4-5

Clarification Statement: Emphasis is on determining cause and effect relationships for how changes to the environment such as deforestation, fishing, application of fertilizers, drought, flood, and the rate of change of the environment affect distribution or disappearance of traits in species.

Assessment Boundary: none

A Peformance Expectation (PE) is what a student should be able to do to show mastery of a concept. Some PEs include a Clarification Statement and/or an Assessment Boundary. These can be found by clicking the PE for "More Info." By hovering over a PE, its corresponding pieces from the Science and Engineering Practices, Disciplinary Core Ideas, and Crosscutting Concepts will be highlighted.

Science and Engineering Practices

Analyzing and Interpreting Data

Analyzing data in 9–12 builds on K–8 experiences and progresses to introducing more detailed statistical analysis, the comparison of data sets for consistency, and the use of models to generate and analyze data.

Constructing Explanations and Designing Solutions

Constructing explanations and designing solutions in 9–12 builds on K–8 experiences and progresses to explanations and designs that are supported by multiple and independent student-generated sources of evidence consistent with scientific ideas, principles, and theories.

Engaging in Argument from Evidence

Engaging in argument from evidence in 9–12 builds on K–8 experiences and progresses to using appropriate and sufficient evidence and scientific reasoning to defend and critique claims and explanations about the natural and designed world(s). Arguments may also come from current scientific or historical episodes in science.

Obtaining, Evaluating, and Communicating Information

Obtaining, evaluating, and communicating information in 9–12 builds on K–8 experiences and progresses to evaluating the validity and reliability of the claims, methods, and designs.


Introduction to Part II: The biology of language evolution: anatomy, genetics and neurology

This article focuses on the evolution of language along with its anatomy, genetics, and neurology. The concepts of instinct and innateness are actually quite useful for describing behaviors that routinely characterize all members of species or at least all species members of specific sex and age classes. Thus, they tend to be favored by scientists with a primary focus on the distinctive behaviors of individual species. To many developmental biologists and developmental psychologists, however, instinct and innateness are fallacious concepts because all behaviors develop through gene-environment interactions. The solution to this dilemma, in Fitch's view, is to abandon the terms “instinct” and “learning” in favor of other terms that more accurately describe the phenomena in question, such as “species-specific” or “species-typical” to describe behaviors routinely displayed by all members of a species, and “canalization” to explain the species-typical gene-environment interactions that produce behavioral regularities. From this perspective, language is a species-specific human behavior that is developmentally canalized via interactions of genes and predictable environmental impacts such as typical adult-infant interactions. In sum, evidence indicates that language evolution probably demanded changes in multiple interacting genes and involved expansions in multiple parts of the brain, as well as changes in the vocal tract and thoracic spinal cord.

Some of us have long assumed that instinct versus learning controversies met their demise back in the 1960s with publications such as ‘How an instinct is learned’ (Hailman 1969) and the insightful behavioural analyses of Robert Hinde (1966). Not so. In Fitch's view (Chapter 13), these controversies continue, both because they reflect interdisciplinary gaps and because of the tendency of scientists to black‐box issues not of their own immediate concern. Concepts of instinct and innateness are actually quite useful for describing behaviours that routinely characterize all members of species or at least all species members of specific sex and age classes. Thus, they tend to be favoured by scientists with a primary focus on the distinctive behaviours of individual species. To many developmental biologists and developmental psychologists, (p. 134) however, instinct and innateness are fallacious concepts because all behaviours develop through gene–environment interactions. The solution to this dilemma, in Fitch's view, is to abandon the terms ‘instinct’ and ‘learning’ in favour of other terms that more accurately describe the phenomena in question, such as ‘species‐specific’ or ‘species‐typical’ to describe behaviours routinely displayed by all members of a species, and ‘canalization’ (Waddington 1942) to explain the species‐typical gene–environment interactions that produce behavioural regularities. From this perspective, language is a species‐specific human behaviour that is developmentally canalized via interactions of genes and predictable environmental impacts such as typical adult–infant interactions.

Although all animals display species‐specific behaviours, most also exhibit behavioural plasticity in response to learning and/or in response to environmental conditions that may directly impact on brain development or physiological status (West‐Eberhard 2003). Some animals can even, if subject to unusual rearing conditions, develop behaviours not considered typical of their species. Great apes reared in human homes or subject to language‐training experiments, for example, develop a number of behaviours not found in wild apes. In other words, dissimilar phenotypes (i.e. observable behaviours and characteristics) can develop from similar genotypes (i.e. genetic endowment), a phenomenon termed phenotypic plasticity. As Számadó and Szathmáry (Chapter 14) note, phenotypic plasticity plays important evolutionary roles. Specifically, those phenotypes which prove adaptive and the genes that facilitate their development are subject to positive selection, hence, increase in the population (see also West‐Eberhard 2003). Ultimately, these phenotypes may become fixed in the population (Baldwin effect Baldwin 1902). If the genes producing them also become fixed, genetic assimilation will have occurred (Waddington 1953).

Each species occupies physical environments that can change in response to numerous external events such as climate change, earthquakes, or volcanic eruptions. Species, however, also modify and create their own environments, and hence the selective pressures that impinge upon them, a process termed niche construction (Odling‐Smee et al. 2003). Although external environmental events have undoubtedly influenced human evolution, niche construction has arguably played an even greater role in shaping the selective forces that help mould the modern human mind, and perhaps the human body as well, because our lineage has repeatedly created and adapted to new technological, cultural, and linguistic environments. It is sometimes thought that genetic change is too slow for our genes and brain to have adapted to selective pressures posed by ever‐changing languages and cultures. Számadó and Szathmáry counter this argument by presenting numerous examples of rapid genetic change in humans and other species. They also argue that the pace of language change, like technological change, was probably considerably slower during Pleistocene times than it is today. The result of the combined processes of potentially rapid genetic change and an earlier, (p. 135) somewhat slower, pace of language change is that genes, languages, and the brain have co‐evolved, and to some extent may be continuing to do so. On the one hand, genes and brains enable language on the other, language change selects for further, linguistically‐conducive, changes in genes and brains.

12.1 Developmental plasticity and genes

Számadó and Szathmáry (Chapter 14) also suggest that some biological systems, such as the immune system, are specifically adapted to enable rapid responses to environmental change. They suggest, for example, that the brain has been specifically shaped by selection to function as a rapid responder to linguistic change (and we would add cultural change as well). This postulate draws clear support, not only from our species' well‐recognized learning and problem‐solving capacities, but also from the plasticity that characterizes all developing and mature mammalian brains. First, during early developmental periods, all mammalian brains routinely overproduce neurons those neurons that fail to achieve full functionality are subsequently pruned (Edelman 1987). In humans, neuronal production primarily occurs prenatally, as does much neuronal pruning. Similarly, all mammalian brains overproduce synapses during certain periods of development. Again, those that fail to achieve full functionality are later pruned. Our species typically overproduces synapses in the first several postnatal years and again just prior to puberty. One unexpected result is that the typical human adolescent has more synapses than most adults, at least in the frontal lobes (Blakemore and Choudhury 2006). Although the production and pruning of neurons and synapses is primarily a maturational phenomenon, these processes never truly cease. New cortical synapses continue to be produced and pruned throughout life, and a region of the brain concerned with declarative and episodic memory (Zito and Svoboda 2002), the hippocampus, continues to produce new neurons throughout life (Eriksson et al. 1998).

These processes have demonstrable functional effects. For example, in rats, final adult brain size as well as performance on laboratory learning exercises varies depending on experience during the maturational process (Bennett et al. 1964). Similarly, humans who practise particular skills such as piano‐playing or taxi‐driving develop enlarged neural structures pertinent to those tasks (Amunts et al. 1997 Maguire et al. 2000). Language‐related functional reorganizations are also known to occur in humans in relationship to environmental inputs. For example, in congenitally deaf subjects who master sign language at a young age, regions of the temporal lobe that normally mediate auditory functions become more attuned (p. 136) to visual input, including visual gestures (Neville 1991). Similarly, the visual neocortex of congenitally blind subjects assumes tactile functions, if such individuals master Braille at a young age (Sadato et al. 1998). Even literacy changes brain functions, and may, in fact, sharpen the neural perception of phonemes (Dehaene et al. 2010). Recognition of the environmentally‐induced developmental plasticity of mammalian brains helps explain why chimpanzees, bonobos, and other apes, reared from infancy in human homes, can, within limits, develop protolanguage‐like behaviours, whereas wild apes and/or apes captured in adulthood usually cannot.

Brain plasticity, of course, has its limits. All brains of a given species strongly resemble each other in overall structure and function. This must reflect considerable genetic programming. As Számadó and Szathmáry note, numerous genes impact on brain development, and these genes appear to evolve at a rapid pace, thereby potentially impacting rapid evolutionary changes in behaviour. Diller and Cann (Chapter 15) focus on specific genes thought to influence the evolution of language and the brain. FOXP2, a regulatory gene, helps determine when and where other genes are expressed. In humans, certain FOXP2 mutations produce orofacial dyspraxia (possibly by disrupting motor sequencing behaviours), some language deficits, and mal‐development of several neural structures (Lai et al. 2003). In other animals, depending on the species, FOXP2 may exhibit increased or decreased activity during periods of vocal learning. Hence, although no evidence indicates that FOXP2 directly controls for vocal behaviour, the gene does, apparently, impact on the development and functions of neural structures that do. Specific human mutations in the FOXP2 gene were once thought to have occurred in the last 120,000 years. Re‐evaluations of the genetic data now suggest a much earlier date of about 1.8 to 1.9 million years ago (Diller and Cann, Chapter 15).

Diller and Cann also review variants of two additional genes that, when mutated in modern humans, result in microcephaly (microcephalin and ASPM). Dysfunctional mutations in these genes result in abnormally small brains. Hence, it has been suggested that both played key roles in the evolutionary enlargement of the brain. Brain development, however, is a complex process involving hundreds, possibly thousands, of genes. Functional disruptions in any of these can cause developmental neural pathologies. This does not mean that earlier, different mutations in the same genes caused increased brain size, only that normal, fully‐functional genes are needed for brain development. Other evidence cited by Diller and Cann, however, indicates that certain variants of ASPM and microcephalin have increased in frequency in the last 37,000 and 5800 years respectively. Some have interpreted this to mean that these genes are currently experiencing positive selection for their roles in brain function or development, but after reanalysing the data, Diller and Cann conclude that the increased gene frequencies could equally well represent genetic drift. In their view, in‐depth analysis also fails to support reports of correlations between the distribution of these genes and tonal (p. 137) languages. Ultimately, Diller and Cann conclude that language evolution is likely to have resulted from interactions of a multiplicity of genes, rather than from a single mutation in a ‘magic’ language gene. In sum, despite increasing research in this area, our understandings of the genetic basis of language and of human‐specific neural developmental pathways remain vague.

Even though human children speak in full sentences by the time they are about 2½ years old, most research on the neurological basis of language focuses on the anatomy of the adult brain and, then, mostly on brain size or on the anatomy of neocortical structures, some of which reach full functionality only in adolescence or later. Brain size, both absolute and relative to body size, did increase steadily from about 2,000,000 to 300,000 years ago (Mann, Chapter 26). It is likely that these size increases were functionally adaptive otherwise, they would have been selected against. Large brains, after all, are metabolically expensive (Aiello and Wheeler 1995). Specific language‐related neural structures have also increased in size in human evolution, as delineated in a number of the chapters in this section. Consequently, increased brain size almost certainly contributed to the evolution of language. However, no one‐to‐one correlation exists between language and overall brain size, and no specific brain size Rubicon separates the linguistically capable from the linguistically inept. Indeed, given that microcephalics do not entirely lack linguistic abilities (Diller and Cann, Chapter 15) it is clear that overall brain size is not the sole determinant of language capacity.

Most investigators have worked on the assumption that language evolution primarily involved the neocortex, either the differential expansion of neocortical areas and connections already present in non‐human primates and/or the addition of new neocortical structures. Gibson (Chapter 16) takes a somewhat different stance. Following on from Gibson and Jessee (1999) and P. Lieberman (1991, 2000, 2002), she reminds us that lesions in structures such as the cerebellum and basal ganglia often produce speech and language deficits. These areas have greatly expanded in human evolution and they mature earlier than many areas of the neocortex (Gibson 1991). In addition, a greater percentage of descending cortical fibres terminate directly on brainstem and spinal cord motor neurons in humans than in monkeys and apes, providing for finer control of lip, tongue, and finger movements (Kuypers 1958). Consequently, neural areas and connections other than those confined to the neocortex deserve far greater scrutiny from the language origins community.

(p. 138) Donald (Chapter 17) also emphasizes the role of neural circuitry involving the basal ganglia, cerebellum, and neocortical areas (especially the premotor and dorsolateral prefrontal cortex). These circuits enable procedural learning, that is, the acquisition of motor skills that require much practice, including those needed for mimesis and tool‐making, both of which, in his view, preceded language evolutionarily (see also Arbib, Chapter 20). Donald further notes that although mimesis is, in large part, a sensorimotor function, the social contexts in which it is used are amodal. Hence, once mimesis became an integral part of human behaviour, through, for example, mime, it would have selected for enhanced amodal cognitive capacities, such as those needed for language and mediated by the inferior parietal and frontal lobes (see also Wilkins, Chapter 19).

Most vertebrate brains exhibit functional lateralization (Rogers and Andrew 2002). In humans, the left hemisphere controls the right arm and hand and, as Hopkins and Vauclair (Chapter 18) note, it is also dominant for language and speech in 96% of right‐handed and 70% of left‐handed individuals. Although it has long been known that individual primates prefer specific hands, until recently it was assumed that population‐wide preferences for the right hand were a uniquely human trait. Indeed, the coincidence of two left hemisphere‐controlled, largely species‐specific human behaviours (right‐handedness and language) has led to hypotheses that cerebral lateralization, language, and right‐handedness evolved together in a causally interconnected manner (Corballis 1993 Crow 2004). Such views long received support from studies indicating that monkeys and apes fail to display population‐level handedness in simple manual reaching tasks. More recently, however, Hopkins' group has found population‐wide right‐handedness in captive chimpanzees, when they were tested on complex manipulative tasks requiring that an object be held in one hand and manipulated in the other (Hopkins 1995).

In Chapter 18, Hopkins and Vauclair also report that captive chimpanzees, bonobos, gorillas, and baboons all exhibit population‐wide biases for the use of the right hand for communicative gestures. In contrast, judging by asymmetrical facial expressions, the majority of vocalizations and facial expressions in non‐human primates are controlled by the right hemisphere. The few exceptions, controlled by the left hemisphere, include marmoset twitters and the novel raspberry sounds and extended food grunts made by some captive chimpanzees. Hence, lateralization in non‐human primates may be greater for communicative gestures than for manipulative behaviours, and for voluntary, as opposed to emotional, vocalizations. These findings suggest that left‐hemisphere dominance for speech and language may have been preceded evolutionarily by left‐hemisphere dominance for voluntary gestures and vocalizations in other primates.

In humans, language and handedness are usually thought to be accompanied by differential expansion of some left‐hemisphere areas, in comparison to similar areas on the right. A literature review by Hopkins and Vauclair finds that Broca's (p. 139) area is somewhat inconsistently expanded in the left hemisphere in both apes and humans. In contrast, the left temporal plane is usually expanded not only in humans, but in apes as well. The left Sylvian fissure is also somewhat longer than the right in both apes and humans. This fissure, which separates the temporal lobe from the parietal and frontal lobes, is surrounded by neocortical areas known to have language functions. In sum, anatomical and behavioural data indicate that neural asymmetry is neither unique to humans nor a specific language specialization. That great apes and monkeys exhibit greater lateralization with respect to gestural usage and voluntary vocalizations may, however, provide clues to possible behavioural precursors to speech and language.

Wilkins (Chapter 19) addresses the anatomy and functions of Broca's area, the POT (parieto‐occipito‐temporal junction), the inferior parietal lobe, and tracts that interconnect these areas. Since one of her aims is the delineation of ape/human neural differences potentially visible in the fossil record, her primary focus is on those species differences that can be seen on the external surface of the brain. This is a critical point, because historically three different parameters have been used to identify neural regions: external anatomy, internal cellular architecture (cytoarchitecture), and function. The three do not always provide identical results. For example, a Broca's area homologue was identified in monkey and ape brains via cytoarchitecture as early as the 1940s (von Bonin and Bailey 1947 Krieg 1954), but most investigators continued to insist, based on external morphology, that Broca's area was unique to humans until the discovery, in the 1990s, of mirror neurons, in what many now accept as the monkey homologue of Broca's area (see Arbib, Chapter 20). Similarly, rhesus monkey and chimpanzee brains contain cytoarchitectonic areas that these earlier neuroanatomists considered homologous to the human POT. Externally, however, the anatomy of the POT region is quite different in apes and humans. In apes, the lunate sulcus separates the occipital lobe from the parietal and temporal lobes, while all three lobes merge in the human brain. Wilkins accepts that much of the parietal cortex and Broca's area have homologues in monkey and ape brains, but she considers the POT to be uniquely human. Nonetheless, she concludes from fossil evidence that the POT evolved early in our lineage, prior to speech. These findings present an evolutionary quandary. The so‐called language areas of the human brain apparently evolved long prior to language. From this, she concludes that language evolution involved exaptation, that is, the re‐appropriation of pre‐existing functions to new uses.

For the most part, Wilkins focuses on the spatial functions of the parietal lobes and their interactions with Broca's and other motor areas in the frontal lobe. Specifically, she notes that that the human POT plays an active role in the formation of modality‐free conceptual structures (see also Coolidge and Wynn, Chapter 21 Donald, Chapter 17). In her view, these functions represent a natural expansion of primate posterior parietal lobe functions, which include the construction of modality‐neutral spatial concepts and the spatial orientation of arm and hand (p. 140) movements. In non‐human primates, these posterior parietal functions are coordinated with motor functions of the frontal lobes to produce object‐related actions. She hypothesizes that the expansion (or emergence) of the POT permitted the enhanced spatial analyses required for the coordination of arm, hand, and thumb movements with respect to tool use and throwing (see also Calvin 1985). Since many linguistic structures are spatially and thematically organized, POT expansion also provided the necessary conceptual structure for critical components of the language function hence, in her view, spatial skills that developed initially in tool‐using situations were later co‐opted for language.

Arbib (Chapter 20) also pursues issues of primate/human neural homologues and neural exaptations. He accepts that the human Broca's area is homologous with similar areas in monkeys and apes, but notes that it has no obvious vocal functions in other species. In contrast, neural areas that do mediate primate vocalizations have no known linguistic role in the human brain. Rather, he posits that mirror neurons found in Broca's area of non‐human primates served as the foundation stones upon which imitation, gesture, and language were built. These neurons fire when a monkey executes a particular manual action and when it observes another individual performing the same action. Mirror neurons thus provide an essential language function—parity that is, assuring that communicator and recipient have similar perceptions. In Arbib's view, mirror neurons serve as essential components of language and imitation, but are not, by themselves, sufficient to mediate behaviours which require the hierarchical integration of multiple actions and concepts. Since the earliest mirror neurons to be identified were related to manual actions, Arbib adopts a gestural model of language origins and delineates how such a system may have evolved. More recent research indicates that mirror neurons are also found in the inferior parietal lobe may represent oral movements as well as manual and may also be of an audiovisual nature. Hence, the mirror neuron story continues to unfold.

Coolidge and Wynn (Chapter 21) focus on the neurological and cognitive correlates of indirect speech, that is, intentionally ambiguous utterances that must be interpreted with regard to social context and that are used primarily in situations that require diplomacy. In their view, indirect speech requires working memory, executive control structures, and theory of mind. Working memory, in turn, is composed of phonological storage capacity, a visual spatial sketchpad and an episodic buffer which allows the contents of phonological storage and the visuospatial sketchpad to be simultaneously held in conscious thought, manipulated, and combined and recombined with respect to each other. Hence, it facilitates the construction of complex plans and mental models. Executive functions monitor these activities via selective inhibition and attention. Since indirect speech is a product of multiple interacting cognitive components, it must also be a product of multiple interacting regions of the brain. In particular, Coolidge and (p. 141) Wynn note the involvement of the inferior parietal and superior temporal lobes and the dorsolateral frontal cortex.

Taken as a whole, the chapters in this section indicate that nearly all higher neural processing centres play some role in the mediation of language or speech. The complexity of the neural interactions required for indirect speech, in particular, suggests that whatever neural changes may have been needed to initiate and sustain protolanguage and/or the language of human infants, fully developed ‘diplomatic’ language capacities reflect the interactions of much of the neocortex. In her paper on ape language (Chapter 3), Gibson notes that great apes fall short of humans in their ability to construct linguistic, technical, and other hierarchies, and it is widely accepted that many aspects of language, most strikingly syntax, are hierarchically structured. Consequently, it would seem of prime interest to determine which neural areas mediate hierarchical abilities. Greenfield (1991) assigned that role to Broca's area. Arbib (Chapter 20) follows her lead. Wilkins (Chapter 19) remarks that the POT is structured to automatically create mental hierarchies. Coolidge and Wynn (Chapter 21) do not use the term ‘hierarchical’, but they do suggest that the ability to hold multiple images in mind in order to combine and recombine them is mediated by the dorsolateral frontal lobe. That the various authors in this section assigned hierarchical processing or components thereof to different parts of the neocortex would appear to validate earlier suggestions by Gibson that the creation of linguistic and other hierarchies, like indirect speech, requires the interactions of multiple cortical processing areas (Gibson 1996a Gibson and Jessee 1999).

Although changes in brain function almost certainly played central roles in language evolution, as MacLarnon notes (Chapter 22), other critical anatomical changes occurred as well. For example, the larynx is lower in humans than in apes and the oral cavity is differently structured. Together, these changes allow humans to produce sounds not readily produced by apes. This vocal tract reorganization may have been facilitated by bipedalism, diet, or a combination of the two. In addition, humans have far greater neural control of their breathing than do apes, and, unlike apes, they have no laryngeal air sacs. MacLarnon suggests that increased control of the respiratory apparatus involved expansion of the numbers of neurons in the thoracic spinal cord. While it is impossible to determine laryngeal position from fossils, the very few hyoid bones that have been found suggest that modern human laryngeal structure, including absent air sacs, may have been (p. 142) present in the common ancestor of Neanderthals and anatomically modern humans, but not in australopithecines. Similarly, fossil vertebrae indicate that both Neanderthals and anatomically modern humans had achieved the modern size of the thoracic spinal cord, but Homo erectus had not (see Wood and Bauernfeind, Chapter 25, for a contrary view on the thoracic cord).

In sum, evidence indicates that language evolution probably demanded changes in multiple interacting genes and involved expansions in multiple parts of the brain, as well as changes in the vocal tract and thoracic spinal cord. Given our current understandings of exaptation, niche construction, the Baldwin effect, and neural plasticity, neural changes probably built upon precursor neurobehavioural functions in non‐human primates and occurred over a lengthy period of time. In some cases both neural and vocal changes may have occurred in response to the selective pressures exerted by language and culture, as opposed to strictly external environmental circumstances see also Bickerton (2009a). Nothing that we know about genetic or neural functions would suggest that language arose in response to a sudden mutation or the sudden appearance of a new neural module.

Kathleen R. Gibson is Professor Emerita, Neurobiology and Anatomy, University of Texas Houston. Her co-edited books include, with Sue T. Parker, Language' and Intelligence in Monkeys and Apes (CUP 1990) with Tim Ingold, Tools, Language, and Cognition in Human Evolution (CUP 1993) with Paul Mellars, Modelling the Early Human Mind (McDonald Archaeological Institute 1996) and, with Dean Falk, Evolutionary Anatomy of the Human Neocortex (CUP 2001). She is the co-editor with James R. Hurford of the series, Oxford Studies in the Evolution of Language.

Maggie Tallerman has spent her professional life in northeast England, at Durham then Newcastle University, where she is currently Professor of Linguistics. Her edited and authored books include Language origins: Perspectives on evolution (OUP, 2005), Understanding syntax (Hodder/OUP, third edition 2001), and The syntax of Welsh (co-authored with Borsley and Willis CUP, 2007). She started working on evolutionary linguistics in case a guy on a train asked her where lanugage came from, though some think her real work is on Welsh.


References

Darwin, C. (1872) The Origin of Species. Sixth Edition. The Modern Library, New York.

Dawkins, R. (1996) The Blind Watchmaker. New York, Norton.

Feynman, R. P. (1985) QED: The Strange Theory of Light and Matter. Princeton, NJ: Princeton University Press.

Freeman, S. and Herron, J. C. (2004) Evolutionary analysis Third edition. Upper Saddle River, NJ: Pearson/Prentice Hall.

Futuyma, D. (1998) Evolutionary Biology. Third edition. Sunderland, MA: Sinauer Associates.

Gould, S. J. (2002) The Structure of Evolutionary Theory. Cambridge, MA: Belknap Press of Harvard University Press.

Mayr, E. (1991) One Long Argument. Cambridge, Harvard University Press.

National Center for Science Education. (2012) "Voices for Evolution: Statements from Scientific and Scholarly Organizations."
A compilation of statements from 109 of the world's largest and most prestigious societies of professional research scientists, on the importance of evolutionary theory.
http://ncse.com/media/voices/science

Rhodes, F. H. T. (1983) "Gradualism, punctuated equilibria, and the origin of species." Nature 305: 269-272.


Watch the video: Evidence for evolution. Biology. Khan Academy (May 2022).


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